This invention relates generally to automatic test equipment, and more particularly to using automatic test equipment to test RF and microwave devices that rapidly switch between different operating frequencies.
Manufacturers of RF and microwave integrated circuits frequently use automatic test equipment (ATE) to verify newly manufactured devices. Testing devices early in the manufacturing process generally reduces manufacturing costs. Therefore, manufacturers preferably test integrated circuits prior to packaging the devices or attaching leads.
Oftentimes, manufacturers categorize integrated circuits based upon tested performance. The more accurately ATE systems can test integrated circuits, the more accurately manufacturers can grade devices across different levels of performance. As manufacturers generally receive higher prices for better-performing chips, accurate testing often leads to increased profits.
FIG. 1 is a simplified illustration of a conventional ATE configuration for testing RF and microwave integrated circuits. As shown in FIG. 1, an RF DUT (device under test) 132 is connected to a test system 100, such as the Catalyst(trademark) test system from Teradyne, Inc., of Boston, Mass. The DUT 132 receives an RF input signal V3 and generates an RF output signal V4. The DUT 132 also receives signals for communicating with the test system 100 via digital I/O 122.
The input signal V3 of the DUT 132 includes a modulation signal V1 and a high frequency carrier signal V2. The modulation signal V1 generally includes a separate, low frequency carrier signal in addition to low frequency modulation components. A signal source, such as an arbitrary waveform generator (AWG) 128, produces the modulation signal V1. An RF source, such as a high-frequency synthesizer 118, produces the high frequency carrier signal V2. A mixer 124 combines the modulation signal V1 and the high frequency carrier signal V2 to produce the DUT input signal V3. Owing to the operation of the mixer 124, the input signal V3 to the DUT 132 includes frequency components that correspond to the sum and difference of the frequency components that constitute the signals V1 and V2. Optionally, a low pass filter is provided at the output of the mixer 124, to filter the components that correspond to the difference in frequencies of the signals V1 and V2.
In response to the input signal V3, the DUT 132 generates an output signal V4 . . . . To measure the output signal V4, the automatic test system 100 employs a second high-frequency synthesizer 120 and a second mixer 126. The second mixer 126 combines the output signal V4 with the output of the second synthesizer 120 (V5) to produce a test signal V6. The test signal V6 includes frequency components that correspond to the sum and difference of the frequencies of the signals V4 and V5. A low pass filter (not shown) is generally provided at the output of the second mixer 126 to filter the frequency components that correspond to the sum of the frequencies of the signals V4 and V5 A high-speed digitizer 130 measures the frequency components that correspond to the difference of the signals by sampling the signal test V6. Operating on the sampled data, the test system 100 performs one or more digital signal processing (DSP) algorithms to characterize the DUT 132. These algorithms may include a test for phase noise of the DUT 132.
To test phase noise, the test system 100 performs a Fast Fourier Transform (FFT) on the samples acquired from the high-speed digitizer 130. Noise components are identified in the resulting power spectrum, and the level of each noise component is measured. The levels of the noise components are then compared with one or more predetermined thresholds. The DUT generally passes the test if the noise levels are below the threshold(s). Otherwise, the DUT generally fails the test.
As shown in FIG. 1, the test system 100 also includes a high-speed digital subsystem 116 (HSD). The HSD 116 receives instructions from the host computer 110 via a computer bus 134. In response to these instructions, the HSD generates accurately timed commands. The HSD 116 conveys these commands, via a timing bus 136, to the Digital I/O 122, the AWG 128, and the digitizer 130. These portions of the test system 100 are constructed to rapidly respond to the commands from the HSD 116. Therefore, the HSD 116 can accurately coordinate events that take place in these portions of the test system 200.
Many commercial devices are available that change their carrier frequencies (i.e., xe2x80x9cfrequency hopxe2x80x9d) at predetermined, regular intervals. For example, certain devices that conform to the xe2x80x9cBlue Toothxe2x80x9d communication standard can be made to change their carrier frequency once every 625 microseconds.
We have recognized that the testing arrangement of FIG. 1 cannot accurately measure the characteristics of these Blue Tooth devices as they frequency hop at their specified rate. As shown in FIG. 1, the synthesizers 118 and 120 of FIG. 1 are programmed by a host computer 110. We have recognized commands from the host computer 110 suffer from timing irregularities, which manifest themselves in timing irregularities in programming the synthesizers. We have found that these irregularities are significant and unpredictable.
The timing irregularities of commands from the host computer 110 generally preclude ATE systems from accurately testing Blue Tooth devices as they are being frequency hopped. For certain tests, it may be possible to momentarily interrupt frequency hopping to test these devices at individual operating frequencies. It is believed, however, that doing so for all tests would negatively impact testing accuracy, because it would subject the DUT to conditions that differ significantly from the DUT""s normal operating conditions.
What is needed, therefore, is a test system that is capable of testing RF and microwave devices accurately, as the devices are being frequency-hopped at their normal rates.
With the foregoing background in mind, it is an object of the invention to test frequency-hopping devices, as the operating frequencies of the devices are varied at their normal frequency-hopping rates.
It is another object of the invention to test frequency-hopping devices without being negatively impacted by the timing irregularities of commands from the host computer.
To achieve the foregoing object and other objectives and advantages, a test system for testing a device under test (DUT) includes first and second high-frequency synthesizers, a mixer, and a dynamic controller. The output of the first synthesizer is coupled to the input of the DUT. The mixer combines the output of the DUT with the output of the second synthesizer to generate a test signal, which the test system can then measure. In response to the dynamic controller, the first and second synthesizers are caused to change their output frequencies in synchronization, at tightly controlled instants in time. As the frequencies of the synthesizers are varied from frequency to frequency, the test system measures the test signal at each frequency. The test system then compares the measurements of the test signal with predetermined limits to determine whether the DUT passes or fails.
Additional objects, advantages, and novel features of the invention will become apparent from a consideration of the ensuing description and drawings.